2009PASP..121..465T

The cataclysmic binary V405 Peg, originally discovered as ROSAT Bright Source (RBS) 1955 , shows a strong contribution from a late-type secondary star in its optical spectrum. This led Schwope et al. to suggest that it is among the nearest cataclysmic binaries. Here we present extensive optical observations of V405 Peg. Time-series spectroscopy shows the orbital period,, to be 0.1776469(7) days , or. We classify the secondary star as M3-M4.5, and estimate its contribution to the light. Astrometry with the MDM 2.4 m telescope gives a parallax, and a relative proper motion of. We employ a Bayesian technique to form a best estimate of the distance from the parallax and other indicators; this yields. The semiamplitude of the secondary stars's radial velocity is, indicating a fairly low orbital inclination if the masses are typical. Extensive time-series observations in the band show the system varying between a minimum brightness level of and states of enhanced activity about 0.2 mag brighter. During the low state, the light curve is dominated by ellipsoidal modulation of the secondary star at a period consistent with the spectroscopic value. In the high state, we detect an additional photometric modulation with amplitude, which occurs in the range 220-280 minutes. The frequency of this modulation appears to be stable for a month or so, but no single period was consistently detected from one observing season to the next. The occurrence of low states can be reconciled with a magnetic cataclysmic variable. While the additional signal could point to an asynchronously rotating white dwarf, our data do not show this signal to be truly coherent. We estimate the system luminosity by combining optical measurements with the archival X-ray spectrum. The implied mass accretion rate is orders of magnitudes below the predictions for the standard angular momentum loss above the period gap. The system may possibly belong to a largely undiscovered population of hibernating cataclysmic variable stars.